Scope, Sequence, and Coordination |
A Framework for High School Science Education |
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Based on the National Science Education Standards |
Heat and the Second Law of Thermodynamics |
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Heat, the Transfer of Thermal Energy, and the Second Law of Thermodynamics NSES Generalization (p. 180) Everything tends to become less organized and less orderly over time. Thus, in all energy transfers, the overall effect is that the energy is spread out uniformly. Examples are the transfer of energy from hotter to cooler objects by conduction, radiation, or convection, and the warming of our surroundings when we burn fuels. This is an overgeneralization that is quite unclear. Everything does not tend to disorder over time. One subsystem can produce order in another subsystem over time, making the one more disordered while the other is ordered. This is what happens in photosynthesis, when glucose is synthesized (atoms made more ordered). The energy entering the system increases the order of the particles in the leaf. What is important is the overall effect. It is the closed system, in which particles interact and into and out of which no energy or mass can enter or leave, that must become more disordered over time. This aspect of energy provides the theoretical framework to explain empirical laws of heat transfer and their connections to mechanical work done in a cycle. This leads to thermodynamic efficiency and the second law of thermodynamics. Applications include heat engines. The entropy aspects of the second law also need to be considered. The impossibility of perpetual motion machines of the first kind and especially of the second kind can now be examined. Grade 9 Temperature, heat, conduction, convection, radiation, insulation, phase change, gas, solid, liquid, freezing point, boiling point, calorie, calorimeter Grade 10 Absorption, reflection, vapor, specific heat, calorimetry, mechanical equivalent of heat Grade 11 Heat of fusion, heat of vaporization Grade 12 Efficiency (thermodynamics), coefficient of performance, order, disorder, entropy Heat added = mass times specific heat times temperature change; Newton=s law of cooling; Wien=s displacement law; Charles= law (to establish the need for absolute temperature); absolute temperature Stefan-Boltzmann fourth power radiation law, thermodynamics, the Carnot cycle, the entropy of systems
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